RSA is an asymmetric public key algorithm that has been formalized in RFC 3447. It is in widespread use in public key infrastuctures (PKI) where certificates (cf. OpenSSL::X509::Certificate) often are issued on the basis of a public/private RSA key pair. RSA is used in a wide field of applications such as secure (symmetric) key exchange, e.g. when establishing a secure TLS/SSL connection. It is also used in various digital signature schemes.